The Rutherfurd Photographic Measures. 153 



Jacoby* to corroborate Wilsing, should be given no weight at the 

 present time. 



On the other hand, it is still an open question whether or not 

 the parallaxes obtained from Rutherfurd measures may not be 

 affected by systematic errors, the nature and origin as well as ex- 

 istence of which are at present unknown. The case of P Gygnif 

 as well as Mrs. Davis' deduction of a similai'ly large parallax 

 from the measures^ of "Bradley 3077 " give room for this suspi- 

 cion. It is for this reason that the confirmation of difference of 

 parallax by Wilsing's measures is all the more instructive. 



46. It should be stated in this connection also, that even if 

 such orbital motion exist, its amplitude is so greatly diminished 

 by this difference of parallax of the two stars as to reduce the 

 sum of the squares of the residuals formed in means for the 22 

 groups of Wilsing's Table on page 885§ from 0.1708 to 0.1052 or 

 by nearly forty per cent. 



In the following Table, are reproduced, in column two, these 

 twenty -two mean residualsj and in column three are given also the 

 mean of the residuals for the same plates from the last column of 

 Table XXI, whereby to facilitate their comparison as to the ef- 

 fect produced by the introduction of the parallax into the equa- 

 tions. 



I have also made a second solution of these 110 equations on 

 the assumption that there might be a term whose coefficient is|| 



tan C cos (p — q) 

 to account for the unequal effect on the two stars of the at- 

 mospheric dispersion. The solution of the equations and the re- 

 sulting residuals are not contradictory of Wilsing's conclusions 

 (from the similarity of the spectra of 61 1 and 61 2 ) that there is 

 no reason for the introduction of this term. In column four are 

 given, however, the means of the residuals resulting from this so- 

 lution. 



*Monthly Notices, Vol. LIV, page 117. See also, Vierteljahrsschrift, for 1891, 

 Vol. 26, p. 146. 



t Astronomical Journal, No. 287 : On the Probable Large Parallax of (5 

 Cygni, by Harold Jacoby. 



X Contribution from the Observatory of Columbia University, New York, 

 No. 14. 



\ Sitzungsberichten, etc. 



|| Publicationen des Astrophysikalischen Observatoriums zu Potsdam, No 36, 

 page 144. 



^Monthly Notices, Vol. LV, page 123. But see also Vol. LVIII, page 83. 



